In a December update first reported by Reclaim the Net, the social media giant amended its hate speech policy to include "statements denying existence" in its definition of "dehumanizing speech or imagery".
It already bars "attacks, including generalizations" on the basis of gender identity, among other protected characteristics, including race and religion.
"We define hate speech as a direct attack on people based on what we call protected characteristics — race, ethnicity, national origin, religious affiliation, sexual orientation, caste, sex, gender, gender identity, and serious disease or disability," the policy reads.
It adds: "We define attack as violent or dehumanizing speech, statements of inferiority, or calls for exclusion or segregation."
Facebook allows users to choose from over 50 gender options. Reclaim the Net warned that statements denying the existence of any of these genders could result in a ban on the grounds of "hate speech".
The changes echo recent adjustments made by Twitter to its hateful conduct policy to include misgendering - when an individual refers to a transgender person according to their biological sex as opposed to chosen gender.
The Twitter policy states: "We prohibit targeting individuals with repeated slurs, tropes or other content that intends to dehumanize, degrade or reinforce negative or harmful stereotypes about a protected category. This includes targeted misgendering or deadnaming of transgender individuals."